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Abstract:

A transmission network is comprised of a network management system for
collectively managing and controlling a plurality of transmission devices
coupled mutually through transmission routes and the transmission network
as well. The network management system includes a plane management table
adapted to manage transmission planes defined as a set of paths in the
transmission network, and the plane management table has the function to
set and manage a transmission plane (working plane) applied during normal
operation and besides, a single or a plurality of transmission planes
(protection planes) applicable in the event of occurrence of a fault in
the transmission network. Then, when a fault occurs in the transmission
network, the network management system changes the applied plane to a
suitable transmission plane.

Claims:

1. A transmission network comprising: a network management system for
managing and controlling the transmission network constituted by a
plurality of transmission devices coupled mutually through transmission
routes, wherein said network management system includes a plane
management table adapted to manage transmission planes defined by a set
of paths in said transmission network, said plane management table having
the function to set and manage a working plane applied during normal
operation and besides, a single or a plurality of protection planes
applicable in the event of occurrence of a fault in said transmission
network so that when a fault occurs in said transmission network, the
applied plane may be changed to a suitable transmission plane.

2. The transmission network according to claim 1, wherein a plane optimal
for a case of simultaneous occurrence of faults in said transmission
devices and said transmission routes belonging to a geographical zone in
said transmission network is set as said protection plane in said plane
management table.

3. The transmission network according to claim 1, wherein in addition to
a path belonging to said working plane, a path belonging to said
protection plane is also monitored for its status constantly so as to
reflect the result of monitoring upon said plane management table.

4. The transmission network according to claim 1, wherein said plane
management table memorizes, in mutually corresponding relationship,
identification numbers of said working plane and said protection plane,
pieces of information indicative of all paths belonging to the respective
planes and fault influence degrees indicative of degrees of influences by
faults of the respective planes.

5. The transmission network according to claim 4, wherein the number of
paths which are interrupted is used for calculating said fault influence
degree.

6. The transmission network according to claim 4, wherein the number of
interrupted paths weighted according to their preference degrees is used
for calculating said fault influence degree.

7. The transmission network according to claim 4, wherein said network
management system constantly compares a fault influence degree of said
working plane with that of said protection plane and when a plane having
the minimal fault influence degree differs from a plane applied
presently, the plane having the minimal fault influence degree is
selected as the plane to be applied.

8. The transmission network according to claim 1, wherein in case after
the applied plane is changed to a suitable plane in the event of
occurrence of a fault in said transmission network, a bypass exists which
is associated with an interrupted path and does not have an adverse
influence upon paths normally passable, the interrupted path is relieved
by using said bypass.

9. The transmission network according to claim 1, wherein in association
with paths belonging to said working plane, a protection path to be used
in the event of occurrence of a fault of a normally used working path is
set in advance, switchover in a unit of path is carried out at the time
of occurrence of a fault and, when the result of the switchover is in a
status unsuitable for the overall network configuration, switchover in a
unit of plane is carried out.

10. The transmission network according to claim 9, wherein when, in an
applied plane, a path exists by which any of said working path and said
protection path is interrupted, the overall network configuration is so
judged as to be in improper status and switchover in a unit of plane is
carried out.

11. The transmission network according to claim 9, wherein when, in an
applied plane, a transmission route exists in which congestion occurs,
the overall network configuration is so determined as to be in improper
status and switchover in a unit of plane is carried out.

12. A transmission network management scheme for managing a transmission
network comprised of a network management system adapted to collectively
manage and control a plurality of transmission devices coupled mutually
through transmission routes and the transmission network, wherein said
network management system includes a plane management table adapted to
manage transmission planes defined by a set of paths in said transmission
network, said plane management table having the function to set and
manage a working plane applied during normal operation and besides, a
single or a plurality of protection planes applicable in the event of
occurrence of a fault in said transmission network so that when a fault
occurs in said transmission network, the applied plane may be changed to
a suitable transmission plane.

13. The transmission network management scheme according to claim 12,
wherein a plane optimal for a case of simultaneous occurrence of faults
in said transmission devices and said transmission routes belonging to a
geographical zone in said transmission network is set as said protection
plane in said plane management table.

14. The transmission network management scheme according to claim 12,
wherein said plane management table memorizes, in mutually corresponding
relationship, identification numbers of said working plane and said
protection plane, pieces of information indicative of all paths belonging
to the respective planes and fault influence degrees indicative of
degrees of influences by faults of the respective planes.

15. The transmission network management scheme according to claim 14,
wherein the number of paths which are interrupted is used for calculating
said fault influence degree.

16. The transmission network management scheme according to claim 14,
wherein the number of interrupted paths weighted according to their
preference degrees is used for calculating said fault influence degree.

17. The transmission network management scheme according to claim 14,
wherein said network management system constantly compares a fault
influence degree of said working plane with that of said protection plane
and when a plane having the minimal fault influence degree differs from a
plane applied presently, the plane having the minimal fault influence
degree is selected as the plane to be applied.

18. The transmission network management scheme according to claim 12,
wherein in case after the applied plane is changed to a suitable plane in
the event of occurrence of a fault in said transmission network, a bypass
exists which is associated with an interrupted path and does not have an
adverse influence upon paths normally passable, the interrupted path is
relieved by using said bypass.

19. The transmission network management scheme according to claim 12,
wherein in association with paths belonging to said working plane, a
protection path to be used in the event of occurrence of a fault of a
normally used working path is set in advance, switchover in a unit of
path is carried out at the time of occurrence of a fault and, when the
result of the switchover is in a status unsuitable for the overall
network configuration, switchover in a unit of plane is carried out.

20. The transmission network management scheme according to claim 19,
wherein when, in an applied plane, a path exists by which any of said
working path and said protection path is interrupted, the overall network
configuration is so judged as to be in improper status and switchover in
a unit of plane is carried out.

Description:

INCORPORATION BY REFERENCE

[0001] The present application claims priority from Japanese application
JP2011-184265 filed on Aug. 26, 2011, the content of which is hereby
incorporated by reference into this application.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a transmission network and a
transmission network management system and more particularly, to a
transmission network in which when a fault takes place in a transmission
device or a transmission route inside the transmission network, a process
for switching over the route is carried out and, to a scheme for managing
the transmission network as well.

[0003] Recently, as the amount of data to be transmitted has been
increasing and information service using a network has been becoming
diverse in a transmission network such as Internet and leased line, the
transmission network has been required of compatibility between increase
in capacity and assurance of reliability. One of factors indicative of
the reliability the transmission network has is to suppress the influence
upon service to minimum in the event that a fault takes place in the
transmission device or transmission route inside the transmission
network. Accordingly, many transmission networks are each implemented
with a route control scheme adapted to execute transmission by using a
route which bypasses a faulty spot in the event that a fault occurs.

[0004] Conventionally, the strategy for controlling a signal transmission
path inside the transmission network is typified by a static path control
scheme and a dynamic path control scheme.

[0005] In the static path control scheme, a signal is transmitted on a
path which is predetermined by a network manager and this type of scheme
has been used widely in the conventional synchronous transmission
network. The static path control scheme adopts the path protection
switchover function as a technique for reducing the influence during the
occurrence of a fault. According to the aforementioned function, in
addition to a normally used path (working path), a path (protection path)
used as a bypass at the time of the occurrence of a fault is set in
advance and when a fault takes place, switchover to the protection path
is conducted at a high speed. In order for the switchover to the
protection path to be carried out upon the occurrence of a fault on the
working path, the occurrence of the fault on the path needs to be
detected, and such detection can be materialized through constant
monitoring of faulty paths pursuant to the conventional OAM (operation
administration and maintenance) function.

[0006] The dynamic path control scheme in which each of the transmission
devices searches and selects by itself a passable route is mainly used in
an asynchronous packet transmission network such as an IP (Internet
Protocol) network. In the dynamic path control scheme, when a path
working at present becomes faulty and interrupted, the transmission
device searches by itself a passable route to thereby select a bypass.

[0007] Further, a technique for materializing a rapid switchover in the
event of the occurrence of a fault in the packet transmission network
executing dynamic path control is described in JPA-S63-138848 (Patent
Document 1). In the related art aiming at "Making a proper and quick
recovery from a faulty status under control of a small-sized computer
even when the network configuration becomes complicated or when such a
change in configuration as extension is undertaken.", accomplishment of
the object can be realized by "1. A network fault management scheme for a
network configuration having a network local manager and a network
collective manager, wherein a network configuration table defining a
network configuration is provided in the collective manager, and the
local manager is checked for its status by using the network
configuration table so as to detect a fault, and 2. A network fault
management scheme as recited in 1 above, wherein when the result of the
fault detection indicates the occurrence of a fault, the collective
manager commands the local manager to execute switchover of lines and
devices at a fault occurrence spot and at a configurationally related
neighboring spot as well by designating time for switchover, so that the
switchover can be carried out at the designated time."

[0008] The related prior art is for conducting control and switchover in a
unit of path but JP-A-2003-224587 (Patent Document 2) is for conducting
control and switchover in a unit of network configuration. The related
art has an object of "Providing a line relief method for improving the
effect of relief by considering the importance of line when relieving a
line on which a fault takes place in a network of mesh format, and
providing a highly reliable network adopting the method.", and the object
is accomplished by "Lines are allotted with parameters in compliance with
the degree of importance and in all of faulty cases, the importance is
judged when carrying out relief. If a fault occurs on a line of high
importance but no substitution therefor is present, a line of low degree
of importance free from any fault is deleted and the line of high
importance degree is allotted to the line spot for the sake of relief."

SUMMARY OF THE INVENTION

[0009] Most of the related arts are of a scheme for conducting control and
switchover in a unit of path. In using the scheme, the path switchover
process at the time of fault occurrence and the status after switchover
as well are optimum for an individual path subject to a fault (partially
optimum) but are not always optimum for the overall network (totally
optimum). This point is exposed when a fault of large scale being
affected by, for example, a disaster takes place.

[0010] For example, in the case of static path control, for the sake of
preventing a bias and congestion of use bands from occurring in respect
of individual paths after switchover of all switchover patterns has been
conducted, network working which assumes the most sever one of presumable
cases becomes necessary and consequently, utilization factor of network
band will be degraded remarkably. Further, a path for which both a
working path and a protection path become faulty is interrupted even when
a different passable bypass exists.

[0011] The dynamic path control is said to be highly effective to deal
with a fault in point of keeping continuity but it searches a bypass
after the occurrence of the fault and is problematic in that it has no
knowledge of the congestion condition and the efficiency of communication
the bypass to be selected concerns. Consequently, in the course that the
individual transmission devices search and select passable routes during
the occurrence of a fault, congestion occurs even in normal routes,
resulting in generation of switchover in wide range, and much time is
consumed before completion of switchover and so, paths to be eventually
selected will be biased or localized. Even using the technique described
in Patent Document 1, calculation of a suitable network configuration
must be conducted as necessarily at the time of fault occurrence and
therefore, in the event of a large scale fault, much time is considered
to be necessary especially for calculation. Further, guarantee against
the pass localization and the presence of congestion as a result of
changing the network configuration is not promised.

[0012] When using the technique described in Patent Document 2, switchover
to an optimum network configuration can be materialized by conducing
calculation of a proper network configuration with the fault conditions
in mind. But, as the network configuration becomes complicated and time
to calculate an optimum network configuration increases, there arises a
problem that the time to switchover increases. Further, guaranteeing the
normality of a path to be used after switchover is not referred to and
when a route unused before switchover is used after the switchover,
guaranteed normality of the route now in use is not promised.

[0013] In view of the above, it is an object of the present invention to
provide a scheme which can materialize change of the overall network to a
proper configuration steadily and speedily even in the event that a large
scale fault takes place in the transmission network.

[0014] A transmission network is configured by using a network management
system adapted to collectively manage and control not only a plurality of
transmission devices connected mutually through transmission routes but
also the transmission network. The network management system comprises a
plane management table for managing a transmission plane defined by a set
of transmission routes (paths) inside a transmission network, and the
plane management table has the function to set and manage a transmission
plane applicable during normal operation (working plane) and besides, a
single or a plurality of transmission planes applicable in the event of
occurrence of a fault inside the transmission network (protection plane).
Then, at the time a fault occurs in the transmission network, the network
management system instructs the individual transmission devices to change
the applied plane to a proper transmission plane and to switch over the
route of path to the path setting adapted for the plane after changing.

[0015] According to the present invention, when a fault takes place in the
transmission network, a change of the overall network configuration to a
proper configuration (plane switchover) can be executed steadily and
speedily.

[0016] Other objects, features and advantages of the invention will become
apparent from the following description of the embodiments of the
invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a diagram illustrating an example of configuration of a
transmission network described in embodiment 1 of the present invention.

[0018]FIG. 2 is a diagram illustrating an example of a path configuration
on a working plane in transmission network 10 in FIG. 1.

[0019]FIG. 3 is a diagram illustrating an example of a path configuration
on a first protection plane in transmission network 10 in FIG. 1.

[0020]FIG. 4 is a diagram illustrating an example of a path configuration
on a second protection plane in transmission network 10 in FIG. 1.

[0021]FIG. 5 is a diagram illustrating an example of switchover operation
at the time of the occurrence of a fault in the transmission network 10
in FIG. 1.

[0023]FIG. 7 illustrates an example of a functional block diagram of
network management system 100.

[0024]FIG. 8 is a diagram showing an example of structure of a plane
management table 1001 of network management system 100.

[0025]FIG. 9 is a diagram showing an example of status of the plane
management table 1001 after the occurrence of a fault.

[0026]FIG. 10 is a diagram showing an example of status of the plane
management table 1001 after completion of plane switchover.

[0027]FIG. 11 is a flowchart showing an example of processing in a
network information management controller 1000 in network management
system 100.

[0028]FIG. 12 is a diagram for explaining an example of switchover
operation at the time of the occurrence of a fault in a transmission
network described in connection with embodiment 2 of the present
invention.

[0029]FIG. 13 illustrates an example of a functional block diagram of
network management system 101.

[0030]FIG. 14 is a flowchart showing an example of processing in network
information management controller 1010 in network management system 101.

[0031]FIG. 15 is a diagram illustrating an example of a path
configuration on a working plane in transmission network 11 of FIG. 10.

[0032]FIG. 16 is a diagram illustrating an example of a path
configuration on a first protection plane in transmission network 11 of
FIG. 10.

[0033]FIG. 17 is a diagram illustrating an example of a path
configuration on a working plane in transmission network described in
connection with embodiment 3 of the present invention.

[0034]FIG. 18 is a diagram illustrating an example of switchover
operation at the time of occurrence of a fault in the transmission
network 12 of FIG. 17.

[0035]FIG. 19 illustrates an example of a functional block diagram of
network management system 102.

[0036]FIG. 20 is a diagram showing an example of structure of a plane
management table 1021 of network management system 102.

[0037]FIG. 21 is a flowchart showing an example of processing in a
network information management controller 1010 of network management
system 102.

DESCRIPTION OF THE EMBODIMENTS

[0038] Embodiments of the present invention will now be described with
reference to the accompanying drawings.

1. Embodiment 1

[0039] In the present embodiment, an example of a transmission network
will be described in which a set of a plurality of transmission paths in
a transmission network is managed in terms of a plane by means of a
network management system and when a fault occurs on a working plane used
normally, the working plane is switched to either a protection plane or
the most proper one of a plurality of protection planes which are
prepared in advance. In such an event that faults occur in a plurality of
transmission devices and transmission routes within a range inside the
transmission network and any of highly preferential paths of working
paths and protection paths become interrupted under the conventional
static path control and, as a result, a plurality of path switchovers are
generated to give rise to generation of congestion and localization of
paths inside the transmission network, switchover is conducted swiftly to
a protection plane designed in advance on the assumption that such plural
faults will occur to thereby ensure that a transmission path of high
preference can be assured at its maximum and besides, changing to a
network configuration devoid of congestion and localization of paths can
be materialized by applying the transmission network in the form
according to the present embodiment. Furthermore, in the present
embodiment, even in operation proceeding on a working plane, conditions
of all protection planes are monitored constantly and upon occurrence of
a fault, a plane is selected on the basis of the results of monitoring of
all planes, so that even when a transmission path unused before plane
switchover is brought into use after the plane switchover, normality
after the switchover can be guaranteed to advantage.

[0040] Referring now to FIG. 1, a transmission network 10 according to the
present embodiment is configured as exemplified therein. In the
configuration of transmission network 10, a plurality of transmission
devices 110-1 to 110-11 are coupled mutually through the medium of
transmission routes. The transmission network 10 is coupled to data
centers 120-1 and 120-2 and client terminals 130-1 and 130-2 by way of
access networks 20-1 to 20-4 so as to act as a transmission network for
transmitting data between each of the data center and each of the client
terminals with the help of each of the transmission devices 110.

[0041] Coupling of the data centers to the client terminals 130-1 and
130-2 is not limitative and the client terminal may be coupled with any
server such as a contents server which distributes Web contents or a
server which offers various applications and service. Further, the client
terminals 130-1 and 130-2 may communicate with each other by way of the
transmission network 10.

[0042] It should be understood that in a neighborhood zone 30-1, 30-2 or
30-3 indicated at dotted line, transmission devices 110 are located at
geographically neighboring positions (for example, within a prefecture in
Japan).

[0043] The transmission devices 110-1, 5, 7 and 11 are coupled with the
access networks 20-1, 3, 2 and 4, respectively, to act as edges of
transmission network 10 which will hereinafter be termed edge
transmission devices.

[0044] Also, in the present embodiment, a route for interconnecting two
transmission devices 110 adjacent to each other as described previously
is called a transmission route. For the transmission route, an optical
fiber of 10 gigabits Ethernet (registered trade name), for example, can
be used in the present embodiment.

[0045] Then, a route from an edge transmission device to another edge
transmission device is called a path. If the edge transmission devices
are adjoining, the path may be formed of a single transmission route.
But, if the edge transmission devices are remote from each other and one
or more transmission devices 110 intervene therebetween, the path is
constituted by a plurality of transmission routes.

[0046] In the present embodiment, as a transmission scheme of transmission
network 10, a MPLS-TP (Multi Protocol Label Switching-Transport Profile),
for example, can be used which is noticed as an asynchronous packet
transmission scheme having transmission efficiency and high reliability
for network. This scheme having extensity and transmission efficiency of
the variable length packet transmission technique is added with features
of the conventional synchronous transmission technique such as connection
oriented static path control scheme, the function to detect faults on the
basis of OAM and the QoS (Quality of Service) function of, for example,
band control and preferential control and is standardized as a scheme
capable of dealing with maintenance and working management equivalent to
those by the synchronous transmission network in the variable length
packet transmission network.

[0047] Also, in the present embodiment, as the transmission scheme of
access network 20, an Ethernet (registered trade name held hereinafter)
network and an ATM (Asynchronous Transfer Mode) network can be used.

[0048] Further, the transmission devices 110-1 to 110-11 are coupled to
the network management system 100 by way of a management network 15 so as
to inform the network management system 100 of management information
indicative of, for example, a fault detection status inside the
transmission network 10 and to receive management information such as
path setting instructions from the network management system 100.

[0049] In the transmission network 10, faults are monitored in a unit of
transmission device of a transmission route (a route between two
adjoining transmission devices) and of a path (a route from an edge
transmission device to another edge transmission device), and pieces of
information are collected in the network management system 100.

[0050] The individual fault monitoring operations may be materialized by
known technologies including monitoring a fault in the transmission
device by means of its CPU (Central Processing Unit), monitoring input
interruption and link-down of a link layer of an optical interface of
transmission device coupled to the transmission route and path connection
constant monitoring pursuant to MPLT-TP OAM being in process of
standardization by IETF (Internet Engineering Task Force) and ITU-T
(International Telecommunication Union-Telecommunication Standardization
Sector) in cooperation. For the fault monitoring in a unit of path,
either Ethernet OAM standardized in two frames of ITU-T Y. 1731 and IEEE
802.1ag or MPLS OAM standardized by ITU-TY. 1711 may be used.

[0051] The path inside the transmission network 10 is managed by the
static path control scheme and is set to the individual transmission
devices 110 from the network management system 100. In the present
embodiment, a set of paths settable simultaneously inside the
transmission network 10 and a pattern of combined paths are managed in
terms of concept of a plane. Thus, the network management system 100
manages a plurality of planes assumed as a pattern of combination of
paths which differs in accordance with spots where faults occur by using
a plane management table 1001. In the transmission network 10, in
addition to a plane used for transmission during normal operation
(working plane), planes to be used at the time of failure of the working
plane (protection plane) are set in advance and the working plane and the
protection planes are monitored constantly. When a fault occurs, a path
configuration change in a unit of plane (plane switchover) is carried out
on the basis of a fault detection status on each of the planes.

[0052] By making reference to FIGS. 2 to 11, a path configuration example
on each plane and switchover operation will be described in greater
detail.

[0053] Illustrated in FIG. 2 is an example of a path configuration on a
working plane in the transmission network 10 of FIG. 1.

[0054] A path 40-0 indicated at solid line is a highly preferential path
originating from an edge transmission device represented by transmission
device 110-1 and terminating in an edge transmission device represented
by transmission device 110-11 through relay points of transmission
devices 110-3, 6, 5 and 8, having a guaranteed utilization band of 9 Gbps
(giga-bits/second). A path 41-0 indicated at dashed line is a medium
preference path originating from an edge transmission device represented
by transmission device 110-7 and terminating in the edge transmission
device represented by transmission device 110-11 through a relay point of
transmission device 110-9, having a guaranteed utilization band of 5
Gbps. A path 42-0 indicated at dotted line is a low preference path
extending from the edge transmission device represented by transmission
device 110-1 to an edge transmission device represented by transmission
device 110-5 through a relay point of transmission device 110-2, having a
guaranteed utilization band of 2 Gbps.

[0055] The preferential degree of path designates the degree of preference
for securing a route and a band at the time of occurrence of a fault and
is set to each of the paths in advance. In the drawing, the path is
expressed by a unidirectional arrow for the sake of convenience but
actual data may be transmitted in any of unidirectional direction and
bidirectional direction (This holds in the following figures.)

[0056] Illustrated in FIG. 3 is an example of a path configuration on a
first protection plane to be used in the transmission network 10 of FIG.
1. In the present embodiment, in consideration of the fact that faults
will be liable to occur simultaneously in the transmission devices and
transmission routes constituting the transmission network inside a zone
in the event of a natural calamity such as an earthquake, a path
configuration on protection plane optimal for transmission networks in
zones excepting the fault occurrence range is designed by presuming that
faults will occur in the transmission devices or transmission routes in a
single or plural ones of the neighborhood zones 30-1 to 30-3 in the
transmission network. The optimal path configuration referred to herein
means a path configuration which can preferentially secure a passable
bypass in a transmission network excepting that in the fault occurrence
range and can also secure the transmission band in association with the
highly preferential path 40 and subsequently, can secure a passable
bypass and transmission band for the medium preference path 41 and
thereafter can secure a passable bypass and transmission band for the low
preferential path 42, in order that transmission can be permitted as far
as possible through transmission routes unoccupied at individual timing
points.

[0057] The first protection plane illustrated in FIG. 3 is designed by
using the neighborhood zone 30-1 as an assumptive faulty range. A path
40-1 is a protection system path of highly preferential path 40-0, having
relay points of transmission devices 110-3, 6 and 9. A path 41-1 is
designed as a protection system path of intermediate preference path
41-0, having a relay point of transmission device 110-10. A path 42-1 is
designed as a protection system path of low preference path 42-0 but the
edge transmission device 110-5 in the path is included in the assumptive
faulty range and so, transmission through this path is impossible even by
using a bypass. To deal with such a case, a path similar to the path 42-0
is set in FIG. 3.

[0058] Illustrated in FIG. 4 is an example of a path configuration on a
second protection plane to be used in the transmission network 10 of FIG.
1. The second protection plane is designed by presuming the neighborhood
zone 30-2 as an assumptive faulty range. Paths 40-2, 41-2 and 42-2 are
designed as protection systems of high preference path 40-0, medium
preference path 41-0 and low preference path 42-0, respectively. To add,
both the high preference path 40 and low preference path 42 must route
through the transmission devices 110-1, 2 and 5 but in the present
embodiment, the transmission band the single transmission route can use
is 10 Gbps and therefore, in accordance with the preferential degrees, 9
Gbps and 1 Gbps guaranteed bands are set to the high preference path 40-2
and low preference path 42-2, respectively.

[0059] In the present embodiment, the two examples of protection plane
design are described in which the assumptive faulty range in FIG. 3
differs from that in FIG. 4. By setting more protection planes based on a
similar design rule, changes of network configuration conforming to
generation of faults in various ranges inside the transmission network
can be materialized. In the present embodiment, the protection plane is
described as being designed in advance at the time that the network
configuration is designed but by practicing design of a protection plane
even after starting working of the transmission network and by adding
setting to the network management system 100 and individual transmission
devices at desired time, more faulty patterns can be dealt with to
improve the reliability of the network continuously.

[0060] Turning to FIG. 5, there is illustrated an example of switchover
operation when a fault takes place in the transmission network of FIG. 1.
In this example, an operation will be described in which a fault occurs
in the neighborhood zone 30-1 and the selection plane is changed from the
working plane of FIG. 2 to the first protection plane of FIG. 3. In the
present embodiment, fault monitoring is constantly carried out for not
only paths on the working plane but also paths on the protection plane
and a suitable plane is selected by using fault influence degrees
calculated in respect of individual planes on the basis of fault
detection information in a unit of path.

[0061] When a fault occurs in the neighborhood zone 30-1, the high
preference path 40-0 and low preference path 42-0 on the working plane
are interrupted and a transmission device though which these paths route
detects a fault on the path by using the known OAM technique such as
MPLS-TP or Ethernet to report it to the network management system 100 as
indicated at S-110. The network management system 100 reflects the fault
information upon the plane management table 1001 to perform calculation
and comparison of fault influence degrees of the individual planes and on
the basis of the results of calculation and comparison, selects the first
protection plane as a suitable plane in this instance as indicated at
S-120.

[0062] On the basis of the result of selection, the network management
system 100 instructs the individual transmission devices 110 to change
planes as indicated at S-130. In the case of this example, switchover
from the working plane to the first protection plane is instructed. Each
of the transmission devices 110 in receipt of the plane change
instruction executes changing the selection plane on the basis of the
instruction as indicated at S-140. The functional blocks of the
transmission device 110 and network management system 100 for
materializing the present operation will be described hereunder in
greater detail by making reference to FIGS. 6 and 7.

[0063] In the present embodiment, pieces of setting information of the
individual planes are shared by the network management system 100 and
transmission device 110 and switchover is conducted on the basis of the
instruction to change the plane. The setting information of individual
planes the transmission device 110 holds is information which indicates,
in response to identifiers of received frame and packet, for example, as
to which transmission route these frame and packet are transmitted to on
the plane selected at present, and corresponds to a transfer table 11302
to be described later.

[0064] Alternatively, setting information associated with a plane may be
managed by only the network management system 100 and the switchover may
be instructed when the network management system 100 is caused to issue a
path setting change concomitant with the plane change to the individual
transmission devices. In this case, the network management system 100
prepares, from path setting associated with the selected plane, an
instruction concerning setting of a path to be instructed to the
transmission device 110. In such an instance, the existing device can be
used as the transmission device 110.

[0065] Turning now to FIG. 6, the edge transmission device 110 is
illustrated in functional block diagram form. The transmission device 110
includes interfaces (hereinafter abbreviated as IF's) 1110-1 to 1110-m
for transmission and reception as well of packets to and from
transmission routes 10a-1 to 10a-m belonging to the transmission network
10 and IF's 1120-1 to 1120-n for transmission and reception as well of
packets to and from transmission routes 20a-1 to 20a-n belonging to the
access network 20. Frame processing blocks 1111-1 to 1111-m and frame
processing blocks 1121-1 to 1121-n apply processes to be described later
to frames received from the individual IF's and to frames transmitted to
the individual IF's, so that the frames can be transferred by means of a
transfer processing block 1130 to frame processing blocks connected to
destination IF's of received frames. Also, by means of a monitoring
control block 1140 coupled to the management network 15, communication of
fault detection information and path setting information is executed. In
the present embodiment, the individual frame processing blocks are
connected to the individual IF's in one to one relation but the frame
transmission and reception process to and from a plurality of IF's may
structurally be conducted by means of a single frame processing block.

[0066] The individual frame processing blocks 1121-1 to 1121-n execute
processes similar to each other and therefore, operation will be
described by way of example of construction of one of them, that is,
frame processing block 1121-1. The frame processing block 1121-1 includes
a received frame processor 11210 and a transmission frame processor
11211. The received frame processor 11210 identifies an Ethernet frame
and an ATM cell transmitted from the access network 20 and capsules them
to a MPLS frame which in turn is transmitted to the transfer processing
block 1130. The transmission frame processor 11211 receives a frame from
the transfer processing block 1130, removes a MPLS header from it and
transmits a resulting frame to the access network.

[0067] Each of the frame processing blocks 1111-1 to 1111-m is a block for
performing a similar process and so, operation will be described by
taking the construction of one of them, that is, the frame processing
block 1111-1, for instance. The frame processing block 1111-1 includes a
received frame processor 11110, a transmission frame processor 11111, an
OAM terminator 11112, a fault detector 11113 and an OAM inserter 11114.
The received frame processor 11110 identifies a MPLS frame transmitted
from the transmission network 10 so that an OAM frame may be transferred
to the OAM terminator 11112 and user data may be converted into a MPLS
label as necessary and then transferred to the transfer processing block
1130. The OAM terminator 11112 judges, through the known method, the
presence or absence of a fault in a unit of path on the basis of the
received OAM frame and informs the fault detector 11113 of the result.
Receiving from the OAM terminator 11112 information indicative of the
fault in a unit of path and information indicative of physical link
interruption from the IF 1110-1, the fault detector 11113 informs a
monitoring control block 1140 of these pieces of information and as
necessary, instructs the OAM inserter 11114 to transfer the fault
information in the form of an OAM frame. The OAM inserter 11114 operates
to constantly insert an OAM frame for monitoring continuity and as
necessary, inserts an OAM frame for transferring the fault information
and an OAM for testing. The transmission frame processor 11111 executes
scheduling of user data from the transfer processing block 1130 and OAM
frame from the OAM inserter 11114 and transfers them to the IF 1110-1.

[0068] The transfer processing block 1130 includes a transfer processor
11300. a table selector 11301, transfer tables 11302-1˜11302-x and
a transfer table manager 11303. By consulting a transfer table 11302
selected by the table selector 11301 on the basis of label information of
a MPLS frame received from each of the frame processing blocks, the
transfer processor 11300 executes transfer of the frame to a frame
processing block to be connected to a destination IF corresponding to
label information.

[0069] Each of the transfer tables 11302-1 to 11302-x is a table for
managing frame identification information such as MPLS label and
destination IF information of a received frame by making correspondence
to a path, and the individual transfer tables correspond to pieces of
information on individual planes the network management system 100
manages. In other words, the transfer device 110 holds the transfer
tables 11302 corresponding to setting of individual paths on each of the
planes the network management system 100 sets. Then, by consulting a
transfer table corresponding to a plane selected at present in response
to instructions from the network management system 100, the table
selector 11301 carries out setting of the transfer processor 11300.

[0070] The transfer table manager 11303 is a block for managing the table
selector 11301 and transfer tables 11302-1 to 11302-x and by receiving
management information reported by way of the management network 15 and
monitoring control block 1140, executes change of selection by the table
selector 11301 and addition/edition of the transfer table 11302.

[0071] The monitoring control block 1140 includes a fault information
manager 11400, a management information controller 11401 and an IF 11402
coupled to the management network 15. The fault information manager 11400
collects pieces of fault detection information in a unit of path and in a
unit of physical port reported from the frame processing block and pieces
of fault detection information inside the device and informs the
management information controller 11401 of these pieces of information
and as necessary, instructs the fault detector in frame processing block
to transfer pieces of fault information. The management information
controller 11401 transfers the fault detection information reported from
the fault information manager 11400 to the management network 15 via the
IF 11402 and besides, reports management information indicative of plane
switchover instruction and plane setting change from the management
network 15 to the transfer processing block 1130.

[0072] In connection with FIG. 6, the functional block diagram of
transmission device 110 is described by way of example of the
construction of edge transmission device but in the case of a relay
transmission device such as transmission device 110-2 coupled to only the
transmission network 10, the IF 1120 coupled to the access network 20 and
the frame processing block 1121 are unneeded.

[0073] Illustrated in FIG. 7 is a functional block diagram of the network
management system 100. The network management system includes a network
information management controller 1000, a communication processor 1002, a
maintenance interface (hereinafter abbreviated as IF) 1003 and an IF 1004
coupled to the management network 15.

[0074] The communication processor 1002 has a received frame analyzing
unit 10020 for analyzing a frame received from the transmission device
110 and transferring fault detection information and management
information responsive to the plane switchover completion to the network
information managing controller 1000, and a transmission frame generating
unit 10021 responsive to a report from the network information management
controller 1000 to generate plane switchover instructions and management
information indicative of plane setting change and transmit them to the
transmission device 110.

[0075] The network information management controller 1000 includes a plane
management table 1001, a table update processing unit 10001, a fault
influence degree calculating unit 10002, a network status judgment
processing unit 10003 and a network configuration setting controlling
unit 10004. The plane management table 1001 is a table adapted to store
pieces of information of paths belonging to the individual planes and
information indicative of fault detection status, and the network
information management controller 1000 selects a suitable plane
conforming to conditions of a fault on transmission network 10 by using
the information in plane management table 1001. The table update
processing unit 10001 is a block for updating the plane management table
1001 by responding to the fault detection information and plane
switchover completion from the transmission device 110 and receiving the
plane setting addition/change instructions from the maintenance IF 1003.

[0076] The fault influence degree calculation processing unit 10002 is a
block for calculating fault influence degrees plane by plane on the basis
of pieces of fault detection information of paths belonging to the
individual planes in plane management table 1001, that is, information as
to whether the path becomes incapable of transmitting data owing to the
fault, and information indicative of a preferential degree of the path.
The network status judgment processing unit 10003 is a block for
determining an optimal plane by consulting the fault influence degrees of
the individual planes in plane management table. When the optimal plane
is caused to change by the fault, the processing unit 10003 instructs the
network configuration setting controlling unit 10004 to switch over the
plane. The network configuration setting controlling unit 10004 is a
block for reporting to the communication processor 1002 the plane
switchover instructions from the network status judgment processing unit
10003 and the plane setting addition/change instructions from the
maintenance IF 1003.

[0077] The maintenance IF 1003 is an interface for informing a maintainer
of the network management information and reflecting the plane setting
addition/change instructions from the maintainer upon the network
management information and is constituted by a display, a keyboard and
the like. Alternatively, the maintenance IF may be a communication IF
which is coupled to a more upper management network so as to be
controlled remotely. In the present embodiment, the plane setting and
addition is conducted via the maintenance IF 1003 but by storing, in the
network management system 100, a processor adapted to execute calculation
of a suitable plane, the plane setting and addition may be executed on
the basis of information from that processor.

[0078] Referring now to FIGS. 8 to 11, the contents of plane management
table 1001 and processing by the network information management
controller 1000 will be described in greater detail.

[0079] An example of structure of plane management table 1001 of network
management system 100 is shown in FIG. 8. In an item of plane 1001-1,
pieces of information for identifying a working plane and a plurality of
protection planes are indicated and in the present embodiment, the
working plane, a first protection plane and a second protection plane are
designated by plane 0, plane 1 and plane 2, respectively. In an item of
selection status 1001-2, it is indicated which plane path configuration
is selected at present by the transmission network 10. In an item of path
1001-3, a set of paths included in each of the planes is indicated,
showing pieces of information for identifying paths included in the
individual planes. In an item of route information 1001-4, details of the
individual paths are indicated in order that a transmission route is
expressed by identification information of a transmission device
representing an edge of a path and identification information of a
transmission device representing a relay point, and a guaranteed band
which is a transmission band the path must guarantee is included. In an
item of preference degree 1001-5, preference degrees of the
aforementioned individual paths are indicated by numerical values and in
the present embodiment, high preference, medium preference and low
preference are designated by 3, 2 and 1, respectively. In an item of
present status 1001-6, OK (devoid of fault) or NG (fault involved) is set
on the basis of the presence or absence of a fault on each of the paths.
In an item of fault influence degree 1001-7, the degrees of faults on the
individual planes are indicated quantitatively and the number of paths
subject to fault occurrence included on a plane is calculated by
weighting it with degrees of preference of the paths. In a method of
calculating a fault influence degree exemplified in the present
embodiment, the sum of preference degrees of paths undergoing NG is
defined as the fault influence degree. When no fault is generated on the
transmission network 10, the present statuses of paths on the planes 0 to
2 are all OK as shown at 1001-6 in FIG. 8 and the fault influence degrees
of the planes 0 to 2 are all 0 as shown at 1001-7 in FIG. 8.

[0080] Shown in FIG. 9 is the status of plane management table 1001 after
a fault has occurred in the neighborhood zone 30-1 illustrated in FIG. 5.
After the occurrence of the fault in the neighborhood zone 30-1, the
present status 10010-040a indicates that the paths 40 and 42 are NG.
Then, the fault influence degree 10011-0a indicates 4 equaling the sum of
3 of preference degree of path 40 and 1 of preference degree of path 42.
The plane 1 on which the path 42 undergoes NG takes a fault influence
degree of 1 pursuant to the preference degree 1 of path 42. The plane 2
on which the paths 40, 41 and 42 undergo NG takes a fault influence
degree of 6 pursuant to the sum of the preference degrees 3, 2 and 1 the
paths 40, 41 and 42 have, respectively. Consequently, the plane 1
undergoing the minimal fault influence degree is determined as the
optimal plane and the plane switchover is instructed.

[0081] The aforementioned calculation method of fault influence degree
10011-0a is a mere example and a different judgment criterion for optimal
plane can be conceivable. For example, when it is thought much of the
fact that a larger number of high preference paths can be made passable
in selecting the plane, extreme weighting may be conducted by making, for
example, 10000 the preference degree of a high preference path, 100 the
preference degree of a medium preference path and 1 the preference degree
of a low preference path. In contrast, when it is thought much of the
fact that a larger number of paths can be made passable irrespective of
the preference degrees in selecting the plane, the preference degrees may
be equalized by making, for example, 1 the preference degree of a high
preference path, 1 the preference degree of a medium preference path and
1 the preference degree of a low preference path.

[0082] The network status judgment processing unit 10003 of network
management system 100 determines the plane 1 as being the optimal plane
and instructs the plane switchover. Subsequently, when finishing the
plane switchover (changing a transfer table to be selected), each of the
transmission devices 110 informs the network management system 100 of the
completion, so that the selection status of the plane 0 can become
unselected as shown at selection status 10012-0a and the plane 1 is
conditioned for selection as shown at 10012-1a in FIG. 10.

[0083]FIG. 11 shows a flowchart of processing by the network management
controller 1000 of network management system 100. When the work
management of transmission network 10 based on the plane management table
1001 is started, the network information management controller 1000
constantly reflects fault information of network upon the plane
management table 1001, executes calculation/comparison of fault influence
degrees plane by plane and carries out switchover of plane as necessary.

[0084] More specifically, the table update processing unit 10001 first
reflects pieces of fault detection information of the individual paths
upon the present status of plane management table 1001 in step (S-) 1001.
Since the presence or absence of faults on the individual paths can be
judged through the existing OAM technique, the present status 1001-6 of
plane management table 1001 is updated in respect of each of the selected
planes and each of the unselected planes on the basis of pieces of
information reported from the individual transmission devices 110.

[0085] Next, on the basis of the present status 1001-6 of plane management
table 1001, the fault influence degree calculation processing unit 10002
calculates fault influence degrees of the individual planes in step 1002.
Thereafter, the network status judgment processing unit 10003 compares
fault influence degrees of the selected planes and all of the unselected
planes with one another in step 1003 and decides, in step 1004, a plane
of the minimal fault influence degree as to whether to be an unselected
plane.

[0086] If the plane of the minimal fault influence degree is determined as
a selected plane, the plane selected at present is determined as optimal
and the plane switchover is not executed, followed by again executing
update of plane management table 1001 in the step 1001. With the plane of
the minimal fault influence degree determined as an unselected plane, the
unselected plane is determined as the optional plane in the present
condition of the network and this plane is selected in step 1005. In
order to reflect the selected plane upon the transmission network, the
network configuration setting controlling unit 10004 instructs, in step
1006, the individual transmission devices 110 to switchover the plane.

[0087] A specified example of the plane switchover process in the
respective transmission devices 110 will now be described.

[0088] Assumptively, an ID of a VLAN assigned to an Ether frame of access
network 20-1 the transmission device 110-1 stores as path 40 is 40 and a
MPLS label the path 40 has in the transmission network 10 is 400. When
the plane 0 in FIG. 8 acts as a working plane, the table selector 11301
of transmission device 110-1 selects a transfer table 11302 corresponding
to the plane 0 and when receiving a frame having the VLAN ID of 40 from
the access network 20-1, the transmission device 110-1 allots the MPLS
level 400 to the received frame to transmit it to the transmission device
111-3.

[0089] Subsequently, when receiving instructions to execute switchover of
the plane 0 to the plane 2 in FIG. 8, for example, from the network
management system 100, the transfer table manager 11303 of transmission
device 110-1 informs the table selector 11301 of the fact that the plane
is changed from plane 0 to plane 2. Then, the table selector 11301
selects a transfer table 11302 corresponding to the plane 2. When
finishing the plane switchover, the transmission device 110-1 transmits
to the network management system 100 a notice of completion.
Subsequently, when receiving the frame having the VLAN ID of 40 from the
access network 20-1, the transmission device 110-1 allots the MPLS label
400 to the received frame to transfer it to the transmission device 111-2
in turn.

[0090] Reverting to FIG. 11, a description will be given. Subsequently, in
step 1007, completion of the plane switchover is judged depending on the
fact that the table update processing unit 10001 has received notices of
plane switchover completion from all of the instructed transmission
devices 110. But, in case an objective transmission device per se
instructed to switch over the plane becomes faulty and operates for fault
detection or fails to respond, the presence or absence of the notice of
plane switchover completion from that transmission device is excluded
from the condition for making a decision, in the step 1007 of judging the
plane switchover completion. When the completion of plane switchover is
determined in the step 1007, the table update processing unit 10001
reflects a selected status of the plane after the switchover upon the
selected condition 1001-2 of plane management table 1001 and returns, in
step 1008, to the process in the step 1001.

2. Embodiment 2

[0091] In the present embodiment, an example of the transmission network
will be described in which when, after the operation of plane switchover
described in embodiment 1 has been executed, a bypass having no influence
upon transmission through other normal paths exists in association with
the interrupted path, the path is so changed as to be passable by using
the bypass. In the embodiment 1, a path configuration status will
sometimes be selected in which even when a bypass exists in association
with the path becoming interrupted after the plane switchover, the bypass
is not used. This inconvenience may take place when a range in which a
fault occurs actually is smaller than a predetermined fault assumptive
range. But, by applying the present embodiment, a bypass can be assured
as far as possible in association with a low preferential path which is
interrupted after a route of a high preferential path has been assured
swiftly through a plane switchover and, consequently, a more suitable
plane can be set.

[0092] Turning to FIG. 12, an example of switchover operation at the time
of fault occurrence on the transmission network 11 according to the
present embodiment will be described. In this example, a fault occurs in
a region 31-1B surrounded by dotted chained line and communication is
interrupted. However, the fault occurrence range assumed in preparing the
protection plane corresponds to the zone 31-1A and is wider than the
actual fault occurrence range 31-1B. Therefore, according to the
operation of embodiment 1, the network management system 101 changes a
selection plane from the working plane illustrated in FIG. 15 to the
first protection plane illustrated in FIG. 16. As a result, in spite of
the fact that the transmission devices 111-5 and 111-8 included in the
assumptive fault range 31-1A can function, a path routing these devices
will not sometimes be used. In this manner, the low preferential path
52-0 indicated at thinner dotted line is interrupted in FIG. 16.

[0093] In the embodiment 2 shown in FIG. 12, the interrupted path 52-0 is
switched over to a bypass 52-0A. This operation will be described
hereunder.

[0094] When a fault occurs in the neighborhood zone 31-1A, the path 50-0
indicated at thin solid line and a path 52-0 indicated at thin dotted
line on the working plane are interrupted, the transmission devices 111
for routing these paths detect the fault and inform the network
management system 101 of the fault in step 111. The network management
system 101 reflects the fault information upon the plane management table
1011 and on the basis of results of calculation and comparison of fault
influence degrees of the individual planes, selects a suitable plane
(first protection plane) in step 121. On the basis of the result of plane
selection, the network management system 101 instructs, in step 131, the
individual transmission devices 111 to change the plane. In the case of
this example, switchover from the working plane to the first protection
plane is instructed. In this instance, another path for relieving the
path 52-0 is not set on the selected protection plane.

[0095] When receiving the plane switchover instruction, each of the
transmission devices 110 carries out selection plane change on the basis
of the instruction in step 141. Thereafter, the network management system
101 searches, in step 151, a bypass for the interrupted path 52-0 to
capture a path 52-0A indicated at thick dotted line which relays the
transmission devices 111-4, 111-7, 111-9 and 111-8 sequentially. The
network management system 101 distributes to the individual transmission
devices 111 information of a new plane including the newly obtained
bypass. Then, the network management system 101 instructs, in step 161,
switchover to a plane on which the path 52-0 is changed to the path 52-0A
and the transmission device 111 in receipt of the instruction conducts
the switchover process in step 171. A functional block and processing of
network management system 101 for materializing the present operation
will be detailed with reference to FIGS. 13 and 14. To add, the present
embodiment can be realized by structuring the transmission device 111 and
the network management table 1011 similarly to the transmission device
110 and network management table 1001 shown in FIGS. 6 and 8,
respectively.

[0096] Illustrated in FIG. 13 is a functional block diagram of the network
management system 101. The network management system 101 includes a
network information management controller 1010, a communication processor
1012, a maintenance IF 1013 and an IF 1014 coupled to the management
network 16. The communication processor 1012, the maintenance IF 1013 and
the IF 1014 coupled to the management network 16 are functional blocks
which conduct similar processes to those by the communication processor
1002 and maintenance IF 1003 the network management system 100 includes
and the IF 1004 coupled to the management network 15, respectively.
Further, the plane management table 1011, fault influence degree
calculation processing unit 10102 and network status judgment processing
unit 10103 the network status management controller 1010 includes are
functional blocks which conduct similar processes to those by the plane
management table 1001, fault influence degree calculation processing unit
10002 and network status judgment processing unit 10003, respectively,
the network management system 100 as shown in FIG. 7 includes.

[0097] A bypass calculation processing unit 10105 of network information
management controller 1010 is a processing unit for searching a bypass
for a path becoming NG status at present by consulting the plane
management table 1011. In respect of the individual transmission routes,
a numerical value obtained by subtracting the sum of guaranteed bands of
paths using the transmission route from the transmission band 10 Gbps is
managed as a residual band and, out of routes existing as transmission
paths between edge transmission devices on the NG path, a route having
the biggest residual band is selected as a bypass. Extraction of the
routes existing as the transmission paths between the edge transmission
devices on the NG path is executed by determining, out of all
transmission routes in the transmission network, transmission routes used
by the NG path but unused by the OK path as abnormal transmission routes
and by calculating transmission routes between edge transmission devices
between on the NG path from a set of normal transmission routes excluding
the abnormal transmission routes.

[0098] Even when, as compared to the essentially guaranteed band of the
path, the residual band of the bypass is insufficient, the residual band
of bypass is set as the guaranteed band of the path. This setting is done
for the sake of having no influence upon the transmission bands of the
existing paths. Since the path to be set with a bypass can be set at the
cost of degenerating its transmission band to the residual band of the
bypass, the total interruption can be avoided at the cost of failing to
assure the guaranteed band.

[0099] In the event that a plurality of paths undergo NG, bypasses can be
assured starting from a bypass for a high preference path by first
searching the bypass associated with the high preference path and
subsequently, searching bypasses associated with residual paths. The
bypass calculation processing unit 10105 uses for a new plane a network
configuration in which bypasses associated with NG paths are assured as
many as possible and instructs the network configuration setting
controlling unit 10104 to add and select the plane.

[0100] The network configuration setting controlling unit 10104 conducts
the process by network configuration setting controlling unit 10004 of
network management system 100 illustrated in FIG. 7 and in addition, when
receiving instructions for addition and selection of a new plane from the
bypass calculation processing unit 10105, instructs the table update
processing unit 10101 to add the plane to the plane management table 1011
and also, instructs each of the transmission devices 111 to add and
select the new plane.

[0101] The table update processing unit 10101 conducts the process by
table update processing unit 10001 of network management system 100
illustrated in FIG. 7 and in addition, when receiving instructions to add
the new plane from the network configuration setting controlling unit
10104, adds the new plane to the plane management table.

[0102] A flowchart showing the process by network information management
controller 1010 of network management system 101 is shown in FIG. 14.
When working management of transmission network 11 based on the plane
management table 1011 is started, the network information management
controller 1010 constantly reflects network fault information upon the
plane management table 1011, conducts calculation and comparison of fault
influence degrees of the individual planes and as necessary, carries out
switchover of plane in steps 1101 to 1104. Details of these processes are
similar to the processes in steps 1001 to 1008 in the network information
management controller 1000 according to embodiment 1 shown in FIG. 11.

[0103] Subsequently, by consulting the plane management table 1011, the
bypass calculation processing unit 10105 confirms, in step 1105, whether
an interrupted path exists on a plane presently selected and searches
whether a bypass associated with the interrupted path and having no
influence upon other normal paths is exists. In the absence of the
bypass, the plane after the plane switchover execution is determined as
an optimal plane and the program returns to the step 1101. In the
presence of the bypass, instructions to newly add and select the plane
configuration using the bypass are reported, in step 1106, to the network
configuration setting controlling unit 10104, which in turn instructs the
table update processing unit 10101 to newly add the plane so that the
plane may be added to the plane management table 1011 and also, instructs
the individual transmission devices 111 to newly add and select the
plane.

[0104] The transfer table manager 11303 of the transmission device 111
instructed by the network management system 101 to add and select the new
plane adds a transfer table 11302 corresponding to the new plane and
instructs the table selector 11301 to select the new transfer table
11302. After finishing selection of the new plane, the transfer table
manager 11303 reports a notice of completion to the network management
system 101.

[0105] Thereafter, the table update processing unit 10101 makes a
decision, in step 1107, as to whether the bypass switchover is completed
by depending on whether the unit 10101 has received notices of plane
addition/selection completion from all of the transmission devices the
unit 1010 has instructed. If determining that the bypass switchover has
been completed in the step 1107, the table update processing unit 10101
selects, in step 1108, the status of selection of the plane on which the
bypass switchover is added in the plane management table 1101.

[0106] In this manner, when after execution of plane switchover, a bypass
having no influence upon the passage and guaranteed band of other normal
paths exists in association with the interrupted path, switchover to a
plane using the bypass is newly carried out, thus making it possible to
conduct a change to a more proper network configuration.

3. Embodiment 3

[0107] In the present embodiment, an example of transmission network will
be described in which when a fault occurs in the transmission network, a
path switchover based on the conventional fast path protection switchover
function is carried out immediately and as a result, if the whole network
configuration is determined unsuitable, the plane switchover described in
embodiment 1 is carried out to optimize the network configuration.

[0108] In the conventional path protection switchover function in the
static path control, a path configuration is general in which when a
fault occurs at a single spot, a path causing any of a working path and a
protection path to be interrupted will not be generated and besides, a
design can be made relatively easily in which the congestion and the
localization of path can be minimized even after path switchover
concomitant with the fault. On the other hand, the switchover described
in connection with embodiment 1 or 2 is a scheme in which the network
management system first collects the pieces of fault information and
subsequently, an optimal one is selected from predetermined planes to
conduct switchover and this scheme is more suitable for an instance
where, for example, so large a fault as to require simultaneous
switchover of a plurality of paths takes place. As will be seen from the
above, the present embodiment presumes the path switchover of a
relatively large scale led by the network management system having
collected the pieces of fault information and is, therefore,
disadvantageous in that the time to switchover is prolonged as compared
to the path protection switchover function in which the transmission
device conducts path switchover by itself or under self-control.

[0109] In the light of the above two points, it can be concluded that in
the case of a fault occurring at a single spot, execution of the fast
switchover based on the conventional path protection switchover function
prefers to the execution of plane switchover. By applying the third
embodiment, the path switchover based on the path protection switchover
function is executed immediately at the time a fault occurs in the
transmission network and if the result is improper for the overall
network configuration, a change to a proper network configuration can be
executed through the plane switchover.

[0110] An example of a path configuration on the working plane of
transmission network according to the present embodiment is illustrated
in FIG. 17. The present embodiment differs from embodiment 1 in that
protection paths are set in advance in association with respective
working paths on a working plane. The protection path is for use in the
path protection switchover function in the conventional static path
control and a protection path system is switched over by the transmission
device 112 by itself. In FIG. 17, a protection path 60-0B indicated at
thin solid line is in association with a path 60-0 indicated at thick
solid line, a protection path 61-0B indicated at thin dashed line is in
association with a path 61-0 indicated at thick dashed line, and a
protection path 62-0B indicated at thin dotted line is in association
with a path 62-0 indicated at thick dotted line.

[0111] An example of switchover operation at the time of occurrence of a
fault in the transmission network 12 according to the present embodiment
is illustrated in FIG. 18. In this example, operation will be described
in which when a fault occurs on a transmission route between transmission
devices 112-5 and 112-8 in transmission network 12, the path 60-0 at thin
solid line is switched over to the protection path 60-0B at thick solid
line. This switchover operation is achieved by the path protection
switchover function representing the conventional technique.

[0112] Edge transmission devices 112-1 and 112-11 detecting the fault on
the path 60-0 through the OAM function execute fast path switchover to
the path 60-0B under self-control as indicated at in S-102. The fault
detection status and path switchover result are collected by the network
management system 102 as indicated at S-112 and are reflected upon the
plane management table 1021 as indicated at S-122. In this manner, relief
of the network is tried in the transmission network 12 according to the
present embodiment pursuant to the fast path transfer in the event of
occurrence of the fault. But, in case both of the working path and
protection path of any path are interrupted owing to a fault of large
scale or congestion occurs in any transmission route owing to generation
of a plurality of path switchovers, thus failing to take a suitable
network configuration through only the path transfer, changing the
network configuration based on the plane switchover as described in
connection with the embodiments 1 and 2 is carried out. The contents of
the plane management table 1201 and the functional block of network
management system 102 for materializing the present operation will be
described in greater detail with reference to FIGS. 19 to 21. To add,
with the transmission device 112 constructed similarly to the
transmission device 110 shown in FIG. 6, the present embodiment can be
materialized.

[0113] Illustrated in FIG. 19 is a functional block diagram of the network
management system 102. The network management system 102 includes a
network information management controller 1020, a communication processor
1022, a maintenance IF (interface) 1023 and an IF 1024 coupled to the
management network 17. The communication processor 1022 and maintenance
IF 1023 and the IF 1024 coupled to the management network 17 are
functional blocks which conduct processes similar to those by the
communication processor 1002 and maintenance IF 1003 and the IF 1004
coupled to the management network 15, respectively, the network
management system 100 as shown in FIG. 7 includes. Further, the table
update processing unit 10201, fault influence degree calculation
processing unit 10202, network status judgment processing unit 10203 and
network configuration setting control unit 10204 included in the network
information management controller 1020 are functional blocks which
conduct processes similar to those by the table update processing unit
10001, fault influence degree calculation processing unit 10002, network
status judgment processing unit 10003 and network configuration setting
control unit 10004, respectively, the network management system 100 as
shown in FIG. 7 includes.

[0114] The fault influence judgment processing unit 10205 in network
information management controller 1020 is a block for deciding the plane
switchover as to whether to be necessary or not and by consulting the
plane management table 1021, decides the status as to whether to be
expressed by "a path on which both a working path and a protection path
are interrupted exists" or "a transmission path in which the sum of
guaranteed bands of accommodated paths exceeds a transmission band of 10
Gbps". When any of the condition is satisfied, a status is determined in
which a large scale fault occurs in the transmission network 12 and
consequently, a suitable network configuration cannot be taken through
only the path switchover and so the plane switchover is necessary.

[0115] An example of the structure of plane management table 1021 of
network management system 102 is shown in FIG. 20. The plane management
table 1021 mainly differs from the plane management table 1001 shown in
FIG. 8 in that in respect of an item of route information 1021-1
concerning a selected plane 0, sub-items of relay point 1021-2 and path
selection status 1021-3 include each pieces of information of working
path and protection path and an item of present status 1021-4 also
includes pieces of information of working path and protection path.

[0116] In the figure, items of present status 1021-4 and path selection
status 1021-3 indicate status which is generated after the path
switchover in the event that the fault occurs as shown in FIG. 18.
Reflected upon the plane management table 1021 in FIG. 20 is a status in
which because of the fault, the present status 10211-060 of the working
path 60-0 of path 60 on the 0 plane undergoes NG and after generation of
a path switchover by the transmission device by itself, a path selection
status 10210-060 of the path 60 occurs in which the protection path 60-0B
is selected.

[0117] To add, in the present embodiment, the most essential configuration
is described in which the protection path is set in advance in
association with each path on only the plane 0 representing the working
plane but in order to make possible the switchover based on the fast path
protection switchover function even after the switchover to the
protection plane, protection paths may also be set in advance in
association with paths on the planes 1 and 2 representing protection
planes or, upon switchover from the working plane to the protection
plane, protection paths associated with the individual paths may be set
additionally.

[0118] A flowchart showing processing by the network information
management controller 1020 of network management system 102 is shown in
FIG. 21. In the present embodiment, if a proper network configuration
cannot be taken by conducting only the conventional path switchover, the
plane switchover will be carried out on specified conditions for
conducting the plane switchover that "a path exists for which the working
path and the protection path are both interrupted" or "a transmission
route exists for which the sum of guaranteed bands of accommodated paths
exceed the upper-limit band." The former condition indicates the presence
of an interrupted path and the latter condition indicates possible
congestion. The upper-limit band indicates the upper limit of
transmissible band in a transmission route and in the present embodiment,
10 Gbps prevails. When working management of transmission network 12
based on the plane management table 1021 is started, the network
information controller 1020 causes the table update processing unit 10201
to constantly reflect network fault information upon the plane management
table 1021 in step 1201. By consulting the plane management table 1021,
the fault influence judgment processing unit 10205 decides, in step 1202,
whether a path exists for which the working path and the protection path
are both interrupted. A decision is also made, in step 1203, as to
whether the sum of guaranteed bands of accommodated paths exceeds the
upper-limit band. If neither the decision in the step 1202 nor the
decision in the step 1203 is satisfied, update of the plane management
table is again carried out in the step 1201, so that if either one is
satisfied, a status for which the plane switchover is necessary is
determined in step 1204 and the plane switchover is tried through
processing in the succeeding steps 1205 to 1211. These processes can be
materialized through similar processes in the steps 1002 to 1008 shown in
FIG. 11.

[0119] As described above, in the embodiment 3, the path switchover based
on the path protection switchover function is carried out instantaneously
at the time a fault occurs in the transmission network and when the
result indicates an unsuitable status for the overall network
configuration, changing to a suitable network configuration can be
conducted through the plane switchover.

[0120] While, in the foregoing embodiments, the path is explained as being
a transmission route between edge transmission devices, these embodiments
can be practiced in a similar way even by considering a transmission
route between arbitrary transmission devices in the transmission networks
10, 11 and 12 as a path.

[0121] According to the foregoing embodiments, in stretching paths between
the transmission devices in the network, plural patterns of combinations
of paths are prepared on the assumption of fault occurring spots in the
network with a view to avoiding the fault occurring spots and when a
fault occurs, one of the prepared plural path combination patterns is
selected and paths are switched over at a time. For example, in the event
that a large earthquake hits a particular area and a fault of large scale
takes place therein, the conventional switchover in a unit of path will
consume much time for restoration or will cause interruption of an
important communication route (path). Contrarily, according to the
present embodiment, the important path can be remedied in a short period
of time.

[0122] It will be appreciated that as explained in connection with FIG.
10, a path of relatively low importance degree will not always be
remedied depending on a selected plane. But an instance will occur in
which even at the cost of interruption of the path of low importance and
urgency, that is, of low preference, a path of high importance needs to
be remedied in a short period of time. For example, in the event of the
occurrence of a disaster of large scale, a communication route (path) for
a system of instructions by the government should not be interrupted. In
such an event, by applying the present embodiment, at least an important
path can keep continuing communications.

[0123] To add, in applying the method according to the embodiment 2, a
path of not so high importance can also be remedied later on.

[0124] It should be further understood by those skilled in the art that
although the foregoing description has been made on embodiments of the
invention, the invention is not limited thereto and various changes and
modifications may be made without departing from the spirit of the
invention and the scope of the appended claims.

Patent applications by Hideki Endo, Kawasaki JP

Patent applications by Masahiko Mizutani, Fujisawa JP

Patent applications by Shinya Fujioka, Kawasaki JP

Patent applications by Yoshihiro Ashi, Yokohama JP

Patent applications by Hitachi, Ltd.

Patent applications in class Packet switching system or element

Patent applications in all subclasses Packet switching system or element